The present invention relates to a communications system such as a cellular radiotelephone communications system. More specifically, the present invention relates to a method and apparatus for providing automated assessment of the quality of service provided by such communications system.
The structure and operation of a typical communications system such as a cellular radiotelephone communications system is known. For example, the structure and operation of a cellular radiotelephone system has been disclosed in publications such as the January 1979 issue of The Bell Systems Technical Journal, and Specification EIA IS-3B entitled xe2x80x9cCellular System Mobile Stationxe2x80x94Land Station Compatibility Specificationxe2x80x9d July, 1984, Electronic Industries Association, both hereby incorporated by reference.
In connection with such cellular radiotelephone communications system in particular, it is known that audio quality analyzers can be employed to measure and report quality information of audio communication channels. Such quality information is used to ensure a high level of quality of cellular service over the service provider""s coverage area. In newer digital cellular radiotelephone systems, however, such audio quality information is not adequate to assess the quality of service provided by such digital systems.
Specifically, the audio quality measurement techniques utilized by such audio quality analyzers use continuous audio tones to measure the quality of the audio communication channel. However, digital cellular radiotelephone systems employ digital voice coders which are designed to efficiently encode and decode human speech, and which actually distort continuous tones. As should be understood, such distorted continuous tones cause measurements of audio quality that are much lower than expected. Accordingly, such distortion renders continuous tone techniques useless when characterizing the quality of service provided by digital radiotelephone systems.
Several techniques to measure the quality of the speech transferred through digital radiotelephone coders have been developed. See, for example, S. Wang, A. Sekey, A. Gersho, xe2x80x9cAn Objective Measure for Predicting Subjective Quality of Speech Coders,xe2x80x9d IEEE Journal on Selected Areas in Communications, vol. 10, no. 5, June 1992, pp. 819-829, hereby incorporated by reference. Briefly, such digital techniques employ samples of human speech to measure the quality of a digital communication channel. Doing so overcomes the distortion problems in digital cellular radiotelephone systems caused by the continuous tone techniques and is also appropriate for measuring the quality of service provided by analog cellular radiotelephone systems. However, and importantly, the human speech sample techniques require exact timing and have been designed for use in a laboratory environment where such exact timing can be closely controlled.
As should be evident, though, a cellular radiotelephone service provider needs to ascertain whether high quality analog and digital service is being provided to all areas where the cellular radiotelephone system provides service, not just in the laboratory environment. Accordingly, a need exists for a method and apparatus for providing automated, in field, geographically located measurements of cellular radiotelephone audio quality employing human speech samples to either verify high quality cellular coverage is present in each area or to identify problem areas which need correction. Moreover, a need exists for such a method and apparatus wherein the measurement of cellular radiotelephone system quality is repeatable between days, weeks, months and even years of testing for statistical accuracy.
The aforementioned needs are satisfied by a system and method for determining a level of quality of a communications medium having an indeterminate delay. The communications medium communicatively couples a transmitting station and a receiving station. The transmitting station transmits over the communications medium a measurement sequence including a synchronization sequence followed by a measurement sample. The transmitted measurement sample has a predetermined beginning point, which is identified by the transmitted synchronization sequence.
The receiving station receives over the communications medium the measurement sequence including the synchronization sequence followed by the measurement sample. The receiving station determines from the received synchronization sequence the beginning point of the received measurement sample. The transmitted measurement sample and the received measurement sample are then compared according to respective beginning points to determine the level of quality of the communications medium.